1. Field of the Invention
The present invention relates to a magnetic recording medium having at least one magnetic layer provided over a non-magnetic support.
2. Description of the Related Art
Magnetic recording media are widely used as recording tapes, video tapes, flexible disks, etc. In the magnetic recording media, a magnetic layer in which a ferromagnetic fine powder is dispersed in a binder is layered on a non-magnetic support. The magnetic recording media are required to have high levels of various properties such as electromagnetic conversion characteristics, transport durability, and transport performance. That is, audio tapes for recording and playing back music are required to have high playback performance of original sounds, and video tapes are required to have excellent electromagnetic conversion characteristics such as playback performance of original images. At the same time as being required to have excellent electromagnetic conversion characteristics as described above, the magnetic recording media are required to have good transport durability.
However, since a magnetic layer obtained by coating a support with a coating solution in which a ferromagnetic fine powder has been dispersed in a binder has a high degree of packing of the ferromagnetic powder and a low value for elongation at break and is brittle, if the magnetic layer is formed without providing an undercoat layer, it might be easily destroyed by the application of mechanical force and peeled off from the support. An undercoat layer is therefore provided on the support so as to make the magnetic layer adhere strongly to the support.
For example, it is known that a compound having a functional group that is cured by radiation such as an electron beam, that is, a radiation curing compound, is used to form an undercoat layer.
For example, it has been proposed that a magnetic recording medium is prepared by forming an undercoat layer using a difunctional aliphatic compound as the radiation curing compound (ref. JP-B-5-57647 (JP-B denotes a Japanese examined patent application publication)). These aliphatic compounds give a cured coating having a glass transition temperature of at most the order of 40° C., and there might be a problem with tackiness during a coating step after the undercoat layer is applied. Furthermore, since such a smooth magnetic layer increases the contact surface between the surface of the magnetic layer and a head, the head is easily contaminated during repetitive sliding.